1. Technical Field
The present invention relates to a rechargeable battery pack for use in an electronic device, and more particularly to a battery pack having a battery protection circuit for protecting a battery from damages induced by short circuits of outside terminals when the battery pack is separated from the electronic device.
2. Related Art
Batteries are widely used in portable electronic devices such as radios, radiophones, notebook computers, video cameras, and cassette tape players etc. Such batteries are typically available in two different types such as those characterized as rechargeable or non-rechargeable and exhibit different end of life voltage characteristics and effective series resistances. Nonrechargeable battery types are those ordinary alkaline batteries that should not be subjected to recharging attempts. Rechargeable battery types are those nickel-cadmium (Ni--Cd), nickel-hydrogen (Ni--H) and nickel metal-hydride (Ni-MH) batteries that should be charged at different rates with different conditions.
Recently, lithium-ion (Li-ion) batteries of organic electrolytic cells have become popular as a power source for portable electronic devices because the battery cells are low weight and overall size with high energy density, low temperature characteristics and stable storage capability. However, Li-ion battery cells are sensitive to overcharging or overdischarging; consequently, no overcharging or overdischarging of any particular cell must be ensured. Generally, Li-ion battery cells are disposed in series and usually housed in a battery pack that is detachable from the electronic device, and are charged differently from other types of rechargeable batteries. Exemplars of contemporary Li-ion battery pack are disclosed in U.S. Pat. No. 5,602,460 for Overcharge Current Protection Circuit And Battery Pack Using Same issued to Fernandez et al., U.S. Pat. No. 5,631,537 for Battery Charge Management Protection Apparatus issued to Armstrong, and U.S. Pat. No. 5,646,508 for Battery Pack Having A Processor Controlled Battery Operating System issued to Van Phuoc et al. Specific battery protection circuits such as disclosed in U.S. Pat. No. 4,342,953 for Battery Protection Circuit issued to Collins, U.S. Pat. No. 4,622,508 for Lithium Battery Protection Circuit issued to Matteau et al., U.S. Pat. No. 5,073,837 for Low Voltage Protection Circuit issued to Baek, U.S. Pat. No. 5,177,426 for Over-Discharge Protection Circuitry issued to Nakanishi et al., U.S. Pat. No. 5,349,280 for Battery Protective Circuit issued to Kim, and U.S. Pat. No. 5,539,299 for Protection Switch For A Battery Powered Device issued to Fernandez et al., may be available to protect the battery cells from overcharging and overdischarging. Other protection elements such as poly-switches and fuses may be used to prevent excessive voltage or current from applying to the battery cells
One significant problem with contemporary battery pack is that positive and negative battery terminals may remain electrically connected even if the battery pack is separated from battery control circuitry. As a result, the positive and negative battery terminals can be inadvertently shorted by a conductor or when in contact with outside conductive material to form resistive body which can severely damage the battery cells. Recent solutions to this problem are disclosed, for example, in U.S. Pat. No. 5,477,130 for Battery Pack With Short Circuit Protection issued to Hashimoto et al., and U.S. Pat. No. 5,608,304 for Battery Protection Circuit And Battery Pack And Apparatus Using the Battery Pack issued to Okumura. Short circuit protection mechanism is incorporated into the battery pack to protect the battery cells from short circuits when the battery pack is removed from the electronic device. While the short circuit protection circuits as disclosed by Hashimoto et al. and Okumura are worthy solutions to the problem, I have noted that alternative and simple circuit configurations are still required for short circuit protection.